1. Field of the invention
The invention relates to a circuit for testing current-voltage conversion amplifier for photodiode (PD), which is referred to as PD in the following.
2. Description of the Prior Art
It is a primary object of the present invention to provide a circuit for testing a current-voltage conversion amplifier having PD without actually exposing light to PD.
FIG. 10 shows a current-voltage conversion amplifier having a PD which are incorporated onto IC. In FIG. 10, the numeral 10 denotes a light sensor, the numeral 12 denotes a PD, 20 denotes a current-voltage conversion amplifier, the numeral 14 denotes a reference supply, the numeral 21 denotes an amplifier, the numeral 22 denotes a feedback resistor. When PD is exposed to the light PD pulls current I from current-voltage conversion amplifier 20 in the light sensor circuit 10. Then the current I is convened into a voltage V at the current-voltage conversion amplifier so that the outputs voltage (Vout) is outputted to an output terminal 11 in proportion to the strength of the light.
In case that PD 12 is a type for pulling current from inverted terminal of amplifier 21 when PD is exposed to the light, the current-voltage conversion amplifier 20 operates so that an output voltage of the output terminal 11 increases in response to the increase of the light intensity.
On the other hand, in case that PD is a type for pouting current into an inverted terminal of the amplifier 21 when IC is exposed to light, the current-voltage conversion amplifier 20 operates so that an output voltage (Vout) of the output terminal 11 decreases as light intensity increases.
Conventionally, characteristics of PD incorporated onto IC is measured by actually exposing light to PD and obtaining an output voltage from the current-voltage conversion amplifier after IC is assembled.
However, when carrying out the test by actually exposing the light to PD, the test equipment for illuminating the light is expensive and complex. Furthermore, it takes a long time for testing, and personnel expenses become high, accordingly there is a problem that a cost of semi-conductor becomes high.